Pythagoras is credited for defining a mathematical equation back in 570-495 BC which gives the understanding that frequency specific vibration is not limited to an eight-note octave. Up to the 12th and 13th centuries, musicians were allowed to find and use frequencies which individually targeted vibrational connections with the human body. But in the 13th and 14th centuries, the Roman Catholic Church started to mandate which frequencies could and could not be used in music composition.
Around 1888, the great opera composer, Giuseppe Verdi, mandated that all symphony orchestras would tune Concert A to 432 Hz. It was late believed (evidence not proven) that scientists went to Adolph Hitler in and around 1937, telling him that if orchestras would tune to 440 Hz instead of 432 Hz, that the listening audience would be more susceptible to subliminal directions. This was in turn given to Joseph Gerble, the propaganda manager of the 3rd Reicht to implement into ever city's orchestra under control of the Reicht.
After WWII, the International Standards Organization (ISO) mandated that concert A for all music be at 440 Hz and has not been changed and rarely questioned. It has only been since Hans Jenny (1904-1972) https://en.wikipedia.org/wiki/Cymatics defined a new term CYMATICS which filmed studies have taken place to understand how energy moves through matter. Modulating frequencies is seen through the simple design of laying a stereo speaker on its back, placing a flat metal plate on top of the speaker, pouring fine sand on top and then turning on an amplifier and frequency generator. As the frequency is modulated up or down, it is only on specific frequencies do we find that the sand forms specific geometric patterns. As the frequencies continue to modulate, the sand dissolves from the patter, back into a blob and then into another geometric pattern. These patterns show frequencies which energy moves through matter. Over the past 8-10 years, we now have new scientific studies of epigenetics https://en.wikipedia.org/wiki/Epigenetics and from here is the application of understanding signal transduction https://en.wikipedia.org/wiki/Signal_transduction